Empa researchers are currently working with a Canadian team to develop flexible, biocompatible nanocellulose sensors that can be attached to the skin. The 3D-printed analytic chips made of renewable raw materials will even be biodegradable in the future.
Nanocellulose is an inexpensive, renewable raw material, which can be obtained in the form of crystals and fibers, for example from wood. Other sources of the material are bacteria, algae or residues from agricultural production. Nanocellulose is not only relatively easy and sustainable to obtain, its mechanical properties allow it to be formed into composite materials that could be used as surface coatings, transparent packaging films or even bottle materials.
Researchers at Empa's Cellulose & Wood Materials lab and Woo Soo Kim from the Simon Fraser University in Burnaby, Canada, focused on nanocellulose’s biocompatibility. Since the material is obtained from natural resources, it is particularly suitable for biomedical research.
With the aim of producing biocompatible sensors that can measure important metabolic values, the researchers used nanocellulose as an "ink" in 3D printing processes. To make the sensors electrically conductive, the ink was mixed with silver nanowires. The researchers determined the exact ratio of nanocellulose and silver threads so that a three-dimensional network could form.
The resultant material resembled a smaller thread of spaghetti. The scientists found that the cellulose nanofibers are better suited than cellulose nanocrystals to produce a cross-linked matrix with the tiny silver wires. "Cellulose nanofibers are flexible similar to cooked spaghetti, but with a diameter of only about 20 nanometers and a length of just a few micrometers," explained Empa researcher Gilberto Siqueira.
The team succeeded in developing sensors that measure medically relevant metabolic parameters such as the concentration of calcium, potassium and ammonium ions. The electrochemical skin sensor sends its results wirelessly to a computer for further data processing.
While the tiny biochemistry lab on the skin—which is only half a millimeter thin—is capable of determining ion concentrations specifically and reliably, the researchers are already working on an updated version.
"In the future, we want to replace the silver particles with another conductive material, for example on the basis of carbon compounds," Siqueira explained. This would make the medical nanocellulose sensor not only biocompatible, but also completely biodegradable.